Zimbabwe's opposition leader Morgan Tsvangirai has withdrawn his challenge to the re-election of president Robert Mugabe.

The withdrawal of the challenge clears the way for 89-year-old Mr Mugabe to claim his seventh term in office - another five years.

He has governed since Zimbabwe gained independence in 1980.

Mr Mugabe won the July 31 ballot with 61 per cent of the presidential vote.

Mr Tsvangirai and his Movement for Democratic Change (MDC) party had challenged the vote calling it "a farce" and claiming widespread fraud.

But he now says he does not have enough evidence to proceed with his challenge in the country's constitutional court, claiming to be blocked from obtaining the information he needs to proceed with his case.

"I can confirm that we have withdrawn the presidential election petition," MDC spokesman Douglas Mwonzora said.

"There are a number of reasons, including the failure by the Zimbabwe Electoral Commission to release critical evidence in this matter."

The decision appeared to end any hope of further action by the MDC through the courts, which Mr Tsvangirai's party have said are dominated by Mr Mugabe's ZANU-PF along with other state institutions in the southern African nation, formerly known as Rhodesia.

Mr Tsvangirai, whose party has been plunged into crisis after its third failure to unseat Mr Mugabe through elections, has dismissed the vote as a "huge fraud" and a "coup by ballot".

In his withdrawal letter to the Constitutional Court, Mr Tsvangirai said the MDC would continue its fight to restore democracy.

"This, sadly, as far as I am concerned entails that the Zimbabwe situation is far from resolved and on my part, as the leader of my political party, I shall endeavour to use all democratic means to bring about the successful resolution of this issue," he said.

Political analysts said Mr Tsvangirai has been careful not to speak about street protests, fearing a crackdown on his MDC leadership by Mr Mugabe's security forces.

Mr Mugabe, emboldened by the election results, has vowed to press on with his plan to have foreign companies in the country turn over majority stakes to locals, a policy analysts said has deterred investment and been a drag on the economy.

Mr Tsvangirai's case withdrawal paves the way for Mr Mugabe, who is attending a summit of the 15-nation Southern African Development Community (SADC) in neighbouring Malawi, to be sworn in for another five-year term.